blue jay, common name for a familiar bird ( Cyanocitta cristata ) of central and E North America, allied to the crow, the raven, and the magpie, belonging to the family Corvidae. Almost a foot (30 cm) long, it is handsome and conspicuous. Its upper parts, including the crest, are grayish violet blue. The wings and tail are bright blue with black and white markings, the neck is collared with black, and the under parts are gray and white. Except during the nesting season it has a raucous cry with hawklike and other imitative sounds. Some winter in their northern range, but many travel south. They feed chiefly on large insects, seeds, and nuts (especially acorns and beechnuts); they also eat eggs and nestlings. When the female blue jay is incubating, she is fed by the male. Blue jays are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Passeriformes, family Corvidae.